Non-planar flash memory array with shielded floating gates on silicon mesas

ABSTRACT

A first plane of memory cells is formed on mesas of the array. A second plane of memory cells is formed in valleys adjacent to the mesas. The second plurality of memory cells is coupled to the first plurality of memory cells through a series connection of their source/drain regions. Wordlines couple rows of memory cells of the array. Metal shields are formed between adjacent wordlines and substantially parallel to the wordlines to shield the floating gates of adjacent cells.

RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.11/363,730, titled “NON-PLANAR FLASH MEMORY ARRAY WITH SHIELDED FLOATINGGATES ON SILICON MESAS,” filed Feb. 28, 2006, now U.S. Pat. No.7,339,228, issued on Mar. 4, 2008, which application is a divisional ofU.S. application Ser. No. 10/916,354 of the same title, filed Aug. 11,2004, now U.S. Pat. No. 7,388,251, issued on Jun. 17, 2008, bothapplications commonly assigned and incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to memory devices and inparticular the present invention relates to a flash memory devices.

BACKGROUND OF THE INVENTION

Memory devices are typically provided as internal, semiconductor,integrated circuits in computers or other electronic devices. There aremany different types of memory including random-access memory (RAM),read only memory (ROM), dynamic random access memory (DRAM), synchronousdynamic random access memory (SDRAM), and flash memory.

Flash memory devices have developed into a popular source ofnon-volatile memory for a wide range of electronic applications. Flashmemory devices typically use a one-transistor memory cell that allowsfor high memory densities, high reliability, and low power consumption.Common uses for flash memory include personal computers, personaldigital assistants (PDAs), digital cameras, and cellular telephones.Program code and system data such as a basic input/output system (BIOS)are typically stored in flash memory devices for use in personalcomputer systems.

Stray capacitance in flash memory cells can cause problems. For example,the capacitance between different floating gates that are close togethercan cause coupling and cross-talk between the floating gates ofneighboring cells. This may also have the effect of reducing memory cellperformance.

FIG. 1 illustrates a cross-sectional view of a typical prior art memorycell array. A typical cell is comprised of a silicon substrate 100. Agate insulator layer 101 is formed on top of the substrate 100. Oxideisolation areas 103 and 104 are formed between the cells. The floatinggates 105 and 106 are formed between the oxide isolation areas 103 and104. An interpoly insulator 107 is formed over the floating gates 105and 106 prior to forming the control gate 110 on top. The memory arrayis comprised of multiple rows 120 and 121 of memory cell transistors.

The capacitances that couple the various components of the array areillustrated as C_(A-D). C_(A) is the row-to-row floating gate straycapacitance. C_(B) is the end-to-end floating gate stray capacitance.C_(C) is the floating gate-to-control gate coupling capacitance andC_(D) is the floating gate-to-substrate coupling capacitance.

The ratio of these capacitive components is determined by thegeometrical dimensions of the facing surfaces constituting thecapacitance and the dielectric constants of the insulator materials. Theends and sides of the floating gates are the plate areas of the straycapacitances. The dielectrics between the side and end areas are theoxide and have the same dielectric constant as the gate oxide. In thecase of NAND flash memory devices, the polysilicon floating gatematerial is thick resulting in large surfaces on the ends and sides ofthe floating gates. The thick floating gate material results in greaterstray capacitances.

For the reasons stated above, and for other reasons stated below whichwill become apparent to those skilled in the art upon reading andunderstanding the present specification, there is a need in the art fora flash memory cell transistor that has reduced coupling betweenfloating gates.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view, along a wordline, of a typicalprior art NAND flash memory cell array.

FIG. 2 shows a top view of one embodiment of a flash memory array of thepresent invention with shielded floating gates on silicon mesas.

FIG. 3 shows a cross-sectional view along axis A-A′ of the embodiment ofFIG. 2.

FIG. 4 shows a cross-sectional view along axis B-B′ of the embodiment ofFIG. 2.

FIG. 5 shows a cross-sectional view along axis C-C′ of the embodiment ofFIG. 2.

FIG. 6 shows a cross-sectional view of fabrication steps for oneembodiment of the present invention in accordance with the array of FIG.2.

FIG. 7 shows a cross-sectional view of additional steps for oneembodiment of the fabrication method of the present invention inaccordance with the array of FIG. 2.

FIG. 8 shows a cross-sectional view of additional steps for oneembodiment of the fabrication method of the present invention inaccordance with the array of FIG. 2.

FIG. 9 shows a cross-sectional view of additional steps for oneembodiment of the fabrication method of the present invention inaccordance with the array of FIG. 2.

FIG. 10 shows a cross-sectional view of additional steps for oneembodiment of the fabrication method of the present invention inaccordance with the array of FIG. 2.

FIG. 11 shows a cross-sectional view of an alternate embodiment of theflash memory array of the present invention.

FIG. 12 shows a block diagram of an electronic system of the presentinvention that incorporates the memory array of FIG. 2.

DETAILED DESCRIPTION

In the following detailed description of the invention, reference ismade to the accompanying drawings that form a part hereof and in whichis shown, by way of illustration, specific embodiments in which theinvention may be practiced. In the drawings, like numerals describesubstantially similar components throughout the several views. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention. Other embodiments may be utilizedand structural, logical, and electrical changes may be made withoutdeparting from the scope of the present invention. The followingdetailed description is, therefore, not to be taken in a limiting sense,and the scope of the present invention is defined only by the appendedclaims and equivalents thereof. The terms wafer or substrate used in thefollowing description include any base semiconductor structure. Both areto be understood as including gallium arsenide (GaAs), germanium,carbon, silicon-on-sapphire (SOS) technology, silicon-on-insulator (SOI)technology, thin film transistor (TFT) technology, doped and undopedsemiconductors, epitaxial layers of a silicon supported by a basesemiconductor structure, as well as other semiconductor structures wellknown to one skilled in the art. Furthermore, when reference is made toa wafer or substrate in the following description, previous processsteps may have been utilized to form regions/junctions in the basesemiconductor structure, and terms wafer or substrate include theunderlying layers containing such regions/junctions.

While the subsequently described embodiments are to a NAND flash memorydevice, the present invention is not limited to such an architecture.For example, using a virtual ground array that is well known in the art,the flash memory array with shielded floating gates can be fabricated ina NOR architecture.

In the NOR configuration, the cells are arranged in a matrix. Thecontrol gates of each floating gate memory cell of the array matrix areconnected by rows to wordlines and their drains are connected to columnbitlines. The source of each floating gate memory cell is typicallyconnected to a common source line. Still other embodiments can use otherarchitectures.

FIG. 2 illustrates a top view of one embodiment of a flash memory arrayof the present invention with shielded floating gates on silicon mesas.The transistors are formed both on the mesas and in adjacent valleysbetween the mesas. Metal shielding prevents coupling between adjacentfloating gates in the same column. Wordlines that connect the rows ofthe array are formed into the valleys between adjacent columns toprevent coupling between floating gates in the adjacent columns.

FIG. 2 illustrates cross-sectional axes that are used to show thestructures of the present invention. A cross-sectional view along axisA-A′ of one embodiment of the present invention is illustrated in FIG.3. A cross-sectional view along axis B-B′ of one embodiment of thepresent invention is illustrated in FIG. 4. Similarly, a cross-sectionalview along axis C-C′ of one embodiment of the present invention isillustrated in FIG. 5.

FIG. 3 illustrates a cross-sectional view along axis A-A′ of theembodiment of FIG. 2. The memory cells are fabricated on a mesa andvalley surface with transistors fabricated both on the mesas and in thevalleys. The cells are not vertical structures but are conventionaldevices with conduction in channels that are parallel to the substratesurface.

The portion of the array illustrated in FIG. 3 is comprised of a columnof cells of which two 330 and 332 are discussed. One cell 330 isfabricated in a valley while the other cell 332 is fabricated on a mesa.The cells 332 on the mesas may be considered to be formed on an upperplane of the substrate and the cells 330 in the valleys may beconsidered to be formed in a lower plane of the substrate.

Source/drain regions 308-310 are doped into the sides of the mesas.These regions 308-310 couple adjacent cells (e.g., cell 330 to 332) ofeach plane together into columns of a NAND architecture. A channelregion exists at the top of each mesa and the bottom of each valley suchthat, during operation of the cells 330 and 332, a channel forms in thechannel region between each pair of source/drain regions 308 and 309 or309 and 310.

In one embodiment, the source/drain regions 308-310 are n+ regions thatare doped into a p-type substrate. However, the source/drain regions andsubstrate of the present invention are not limited to any oneconductivity type.

Gate insulator layers 320 and 321 are formed over the channel regionsand between the source/drain regions 308 and 309 or 309 and 310.Floating gates 322 and 323 are formed over the gate insulators 320 and321. In one embodiment, these are polysilicon floating gates. Alternateembodiments may use nitride or other types of charge storage layers.

Intergate insulator layers 324 and 325 are formed over the floating gatelayers 322 and 323 respectively. Control gates 326 and 327 are formedover the intergate insulators 324 and 325 respectively. The controlgates 326 and 327 are coupled to, or are part of, the wordlines of thememory array as illustrated in subsequent figures showing differentcross-sectional areas. The wordlines couple the rows of the array byfollowing the mesa/valley structure.

For shielding purposes, a metal layer 350-352 is formed between adjacentwordlines in a column of cells of the memory array. The metal 350-352extends along the rows substantially parallel to the wordlines to shieldthe floating gates 322 and 323 of the adjacent cells 330 and 332. Themetal 350-352 is formed deep enough into the structure such that thefloating gates on the mesas are shielded from the lower floating gatesin the valleys. The metal shields can be formed after oxidation of thewordlines and by a metal deposition process.

The gate insulator layer and intergate insulator layer between thepolysilicon gates, as illustrated in FIG. 3, can be high-k dielectrics(i.e., dielectric constant greater than that of SiO₂), compositeinsulators, silicon oxide, or some other insulator. Silicon dioxide(SiO₂) is an insulator with a relative dielectric constant of 3.9. Ahigh-k gate insulator requires smaller write and erase voltages due tothe reduced thickness layer between the control gate and the floatinggate. These dielectric layers may be formed by atomic layer deposition(ALD), evaporation, or some other fabrication technique.

As is well known in the art, ALD is based on the sequential depositionof individual monolayers or fractions of a monolayer in awell-controlled manner. Gaseous precursors are introduced one at a timeto the substrate surface and between the pulses the reactor is purgedwith an inert gas or evacuated.

In the first reaction step, the precursor is saturatively chemisorbed atthe substrate surface and during subsequent purging the precursor isremoved from the reactor. In the second step, another precursor isintroduced on the substrate and the desired films growth reaction takesplace. After that reaction, byproducts and the precursor excess arepurged from the reactor. When the precursor chemistry is favorable, oneALD cycle can be performed in less than one second in a properlydesigned flow-type reactor. The most commonly used oxygen sourcematerials for ALD are water, hydrogen peroxide, and ozone. Alcohols,oxygen and nitrous oxide can also been used.

ALD is well suited for deposition of high-k dielectrics such as AlO_(x),LaAlO₃, HfAlO₃, Pr₂O₃, Lanthanide-doped TiO_(x), HfSiON, Zr—Sn—Ti—Ofilms using TiCl₄ or TiI₄, ZrON, HfO₂/Hf, ZrAl_(x)O_(y), CrTiO₃, andZrTiO₄.

The dielectric layers of the present invention can also be formed byevaporation. Dielectric materials formed by evaporation can include:TiO₂, HfO₂, CrTiO₃, ZrO₂, Y₂O₃, Gd₂O₃, PrO₂, ZrO_(x)N_(y), Y—Si—O, andLaAlO₃.

Very thin films of TiO₂ can be fabricated with electron-gun evaporationfrom a high purity TiO₂ slug (e.g., 99.9999%) in a vacuum evaporator inthe presence of an ion beam. In one embodiment, an electron gun iscentrally located toward the bottom of the chamber. A heat reflector anda heater surround the substrate holder. Under the substrate holder is anozonizer ring with many small holes directed to the wafer for uniformdistribution of ozone that is needed to compensate for the loss ofoxygen in the evaporated TiO₂ film. An ion gun with a fairly largediameter (3-4 in. in diameter) is located above the electron gun andargon gas is used to generate Ar ions to bombard the substrate surfaceuniformly during the film deposition to compact the growing TiO₂ film.

A two-step process is used in fabricating a high purity HfO₂ film. Thismethod avoids the damage to the silicon surface by Ar ion bombardment,such as that encountered during Hf metal deposition using dc sputtering.A thin Hf film is deposited by simple thermal evaporation. In oneembodiment, this is by electron-beam evaporation using a high purity Hfmetal slug (e.g., 99.9999%) at a low substrate temperature (e.g.,150°-200° C.). Since there is no plasma and ion bombardment of thesubstrate (as in the case of sputtering), the original atomically smoothsurface of the silicon substrate is maintained. The second step isoxidation to form the desired HfO₂.

The first step in the deposition of CoTi alloy film is by thermalevaporation. The second step is the low temperature oxidation of theCoTi film at 400° C. Electron beam deposition of the CoTi layerminimizes the effect of contamination during deposition. The CoTi filmsprepared from an electron gun possess the highest purity because of thehigh-purity starting material. The purity of zone-refined startingmetals can be as high as 99.999%. Higher purity can be obtained indeposited films because of further purification during evaporation.

A two-step process in fabricating a high-purity ZrO₂ film avoids thedamage to the silicon surface by Ar ion bombardment. A thin Zr film isdeposited by simple thermal evaporation. In one embodiment, this isaccomplished by electron beam evaporation using an ultra-high purity Zrmetal slug (e.g., 99.9999%) at a low substrate temperature (e.g.,150°-200° C.). Since there is no plasma and ion bombardment of thesubstrate, the original atomically smooth surface of the siliconsubstrate is maintained. The second step is the oxidation to form thedesired ZrO₂.

The fabrication of Y₂O₃ and Gd₂O₃ films may be accomplished with atwo-step process. In one embodiment, an electron gun providesevaporation of high purity (e.g., 99.9999%) Y or Gd metal followed bylow-temperature oxidation technology by microwave excitation in a Kr/O₂mixed high-density plasma at 400° C. The method of the present inventionavoids damage to the silicon surface by Ar ion bombardment such as thatencountered during Y or Gd metal deposition sputtering. A thin film of Yor Gd is deposited by thermal evaporation. In one embodiment, anelectron-beam evaporation technique is used with an ultra-high purity Yor Gd metal slug at a low substrate temperature (e.g., 150°-200° C.).Since there is no plasma or ion bombardment of the substrate, theoriginal atomically smooth surface of the silicon substrate ismaintained. The second step is the oxidation to form the desired Y₂O₃ orGd₂O₃.

The desired high purity of a PrO₂ film can be accomplished by depositinga thin film by simple thermal evaporation. In one embodiment, this isaccomplished by an electron-beam evaporation technique using anultra-high purity Pr metal slug at a low substrate temperature (e.g.,150°-200° C.). Since there is no plasma and ion bombardment of thesubstrate, the original atomically smooth surface of the siliconsubstrate is maintained. The second step includes the oxidation to formthe desired PrO₂.

The nitridation of the ZrO₂ samples comes after the low-temperatureoxygen radical generated in high-density Krypton plasma. The next stepis the nitridation of the samples at temperatures >700° C. in a rapidthermal annealing setup. Typical heating time of several minutes may benecessary, depending on the sample geometry.

The formation of a Y—Si—O film may be accomplished in one step byco-evaporation of the metal (Y) and silicon dioxide (SiO₂) withoutconsuming the substrate Si. Under a suitable substrate and two-sourcearrangement, yttrium is evaporated from one source, and SiO₂ is fromanother source. A small oxygen leak may help reduce the oxygendeficiency in the film. The evaporation pressure ratio rates can beadjusted easily to adjust the Y—Si—O ratio.

The prior art fabrication of lanthanum aluminate (LaAlO₃) films has beenachieved by evaporating single crystal pellets on Si substrates in avacuum using an electron-beam gun. The evaporation technique of thepresent invention uses a less expensive form of dry pellets of Al₂O₃ andLa₂O₃ using two electron guns with two rate monitors. Each of the tworate monitors is set to control the composition. The composition of thefilm, however, can be shifted toward the Al₂O₃ or La₂O₃ side dependingupon the choice of dielectric constant. After deposition, the wafer isannealed ex situ in an electric furnace at 700° C. for ten minutes in N₂ambience. In an alternate embodiment, the wafer is annealed at 800°-900°C. in RTA for ten to fifteen seconds in N₂ ambience.

The above described ALD and evaporation techniques are for purposes ofillustration only. The embodiments of the present invention are notlimited to any one dielectric material or dielectric fabricationtechnique.

FIG. 4 illustrates the cross-sectional view along axis B-B′ of FIG. 2.This view is parallel to the view of FIG. 3 and thus shows a memoryarray column that is adjacent to the column of FIG. 3. The metal shields350-352 extend between and substantially parallel to the wordlines andperpendicular to the columns. This view also shows the alternating planenature of the cells 401 and 402 in that a cell that is in the upperplane in a first column of the substrate is adjacent to a cell in thelower plane in an adjacent column.

The shape and size of the metal shields illustrated in FIGS. 3 and 4 arefor purposes of illustration only. The present invention is not limitedto any one size or shape of metal shield.

FIG. 5 illustrates the cross-sectional view along axis C-C′ of FIG. 2.This view is perpendicular to the views of FIGS. 3 and 4. This viewshows the wordline 500 rows of the memory array. It can be seen that thecontrol gates of FIGS. 3 and 4 are formed into the wordlines 500 thatextend parallel with the metal shields.

The mesa/valley construction and the wordlines provide shielding foradjacent memory cells in a row. As a wordline that connects a row ofmemory cells slopes up and down through the mesas and valleys, itprovides shielding between adjacent floating gates along that wordline.

FIG. 6 illustrates an embodiment for fabricating the non-planar flashmemory array of FIG. 2. An oxide layer 601 and a nitride mask layer 602are formed over the substrate 600. The nitride mask 602 is patterned andetched to produce the embodiment of FIG. 7.

An anisotropic etch process is used to form the mesa/valley structure ofFIG. 7 that leaves portions of the nitride mask 602 and oxide layer 601on the mesas. The anisotropic etch process, in one embodiment, uses apotassium hydroxide (KOH) etch that is highly directional. The KOH etchetches the lower plane 700 of the valley very fast while etching theside planes 701 of the valley at a much slower rate. This directionaletching produces the mesas and valley structure.

An implantation process, illustrated in FIG. 8, lines the valleys withn+ doped regions 800 and 801. The etch process is continued to removethe lowest levels of the valley structure to produce the cross-sectionalview of FIG. 9 where the lower portions 900 and 901 of the valley havebeen etched through to remove the lowest doped regions. The dotted linesindicate the previous valley floors as illustrated in FIG. 8. This etchstep leaves the sidewalls of the valley with the n+ doped source/drainregions. In one embodiment, this etch process is also a KOH anisotropicetch.

FIG. 10 illustrates that the nitride mask layer 602 and oxide layer 601are removed from FIG. 9 in another etch process. The substrate is heattreated to diffuse the source/drain regions. An oxide layer 1003 isformed over the mesa/valley structures in order to form the gate oxidelayer 1003.

A polysilicon layer is deposited over the gate oxide layer 1003. Thislayer is patterned and etched to form the floating gates 1000-1002 ofthe memory cells.

The process can then continue with conventional processing to form theremaining portions of the memory array. For example, the completestructure may be filled with a deposited oxide and planarized bychemical mechanical polishing (CMP). The polysilicon floating gates canbe oxidized or an intergate insulator deposited and the polysiliconcontrol gates and wordlines deposited and separated by masking and anetch process.

The wordlines can be oxidized or covered with a deposited insulatorlayer and the metal shield layers deposited and patterned between thewordlines in order to achieve the structure illustrated in FIGS. 2-5.Metallization for contacts can be accomplished using techniques that arewell known in the art.

In operation, the stepped, non-planar flash memory devices of thepresent invention can be programmed with tunnel injection using positivegate voltages with respect to the substrate/p-well. In anotherembodiment, channel hot electron injection can be used in a programmingoperation. This is accomplished by applying a positive drain voltage(e.g., +6 to +9V) to a first source/drain region, a positive voltage tothe control gate (e.g., +12V) and grounding the second source/drainregion to create a hot electron injection into the gate insulator of thecharge storage region.

An alternate embodiment programming operation uses substrate enhancedhot electron injection (SEHE). In this embodiment, a negative substratebias is applied to the p-type substrate. This bias increases the surfacelateral field near a source/drain region thus increasing the number ofhot electrons. The benefit of such an embodiment is that a lower drainvoltage is required during programming operations. In one embodiment,the negative substrate bias is in the range of 0V to −3V. Alternateembodiments may use other voltage ranges.

For an erase operation, one embodiment uses tunneling with conventionalnegative gate voltages with respect to the substrate/p-well. In anotherembodiment, the control gate is grounded, the drain connection is leftfloating and the source region has a positive voltage applied (e.g.,+12V). Alternate embodiments for erase operations can use other methodssuch as substrate enhanced band-to-band tunneling induced hot holeinjection (SEBBHH) that are well known in the art.

FIG. 11 illustrates an alternate embodiment of the flash memory array ofthe present invention. This embodiment uses alternating pillars andtrenches to shield the adjacent floating gates 1102-1104. A row of thememory array is connected in series by a wordline 1100 that is formedinto the trenches. The wordline provides shielding between adjacentfloating gates due to the wordline flowing over the pillars and downinto the trenches.

FIG. 12 illustrates a functional block diagram of a memory device 1200that can incorporate the flash memory array of the present inventionwith shielded floating gates on silicon mesas. The memory device 1200 iscoupled to a processor 1210. The processor 1210 may be a microprocessoror some other type of controlling circuitry. The memory device 1200 andthe processor 1210 form part of an electronic system 1220. The memorydevice 1200 has been simplified to focus on features of the memory thatare helpful in understanding the present invention.

The memory device includes an array of flash memory cells 1230 that canbe comprised of the non-planar flash memory cells with shielded floatinggates as described previously. The memory array 1230 is arranged inbanks of rows and columns. The control gates of each row of memory cellsis coupled with a wordline while the drain and source connections of thememory cells are coupled to bitlines. As is well known in the art, theconnections of the cells to the bitlines determines whether the array isa NAND architecture or a NOR architecture.

An address buffer circuit 1240 is provided to latch address signalsprovided on address input connections A0-Ax 1242. Address signals arereceived and decoded by a row decoder 1244 and a column decoder 1246 toaccess the memory array 1230. It will be appreciated by those skilled inthe art, with the benefit of the present description, that the number ofaddress input connections depends on the density and architecture of thememory array 1230. That is, the number of addresses increases with bothincreased memory cell counts and increased bank and block counts.

The memory device 1200 reads data in the memory array 1230 by sensingvoltage or current changes in the memory array columns usingsense/buffer circuitry 1250. The sense/buffer circuitry, in oneembodiment, is coupled to read and latch a row of data from the memoryarray 1230. Data input and output buffer circuitry 1260 is included forbi-directional data communication over a plurality of data connections1262 with the controller 1210. Write circuitry 1255 is provided to writedata to the memory array.

Control circuitry 1270 decodes signals provided on control connections1272 from the processor 1210. These signals are used to control theoperations on the memory array 1230, including data read, data write(program), and erase operations. The control circuitry 1270 may be astate machine, a sequencer, or some other type of controller.

The flash memory device illustrated in FIG. 12 has been simplified tofacilitate a basic understanding of the features of the memory. A moredetailed understanding of internal circuitry and functions of flashmemories are known to those skilled in the art.

CONCLUSION

In summary, the flash memory array of the present invention utilizesnon-planar memory cells on silicon mesas that have shielded floatinggates to reduce coupling capacitance between cells while increasingmemory density. Adjacent rows of floating gates are shielded by metallayers that are formed between and substantially parallel to adjacentwordlines on different planes. Adjacent columns of floating gates areshielded by the wordlines that are formed down into the valleys alongthe mesa/valley construction.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement that is calculated to achieve the same purpose maybe substituted for the specific embodiments shown. Many adaptations ofthe invention will be apparent to those of ordinary skill in the art.Accordingly, this application is intended to cover any adaptations orvariations of the invention. It is manifestly intended that thisinvention be limited only by the following claims and equivalentsthereof.

1. A method for programming a non-planar flash memory array, withshielded floating gates, comprising rows and columns of flash memorycells formed in mesas and valleys, each row of memory cells coupled on afirst and a second plane by a wordline and each column of memory cellscoupled on the first and the second plane, each memory cell having apair of source/drain regions formed along mesa sidewalls, a gateinsulator, a floating gate formed over each mesa and in each valley, anda control gate, a metal shield layer extending between adjacentwordlines on different planes, the method comprising: biasing thecontrol gate with a first positive voltage; biasing a first source/drainregion with a second positive voltage; and grounding the remainingsource/drain region to create a hot electron injection into a gateinsulator of the floating gate.
 2. The method of claim 1 wherein thefirst positive voltage is +12V and the second positive voltage is in arange from +6V to +9V.
 3. The method of claim 1 and further includingapplying a negative substrate voltage for substrate enhanced hotelectron injection.
 4. The method of claim 1 wherein the negativesubstrate voltage is in the range of 0V to −3V.
 5. The method of claim 1wherein the negative substrate voltage is applied to a type substrate.6. The method of claim 1 wherein at least one memory cell formed in amesa and at least one memory cell formed in a valley share a commonwordline.
 7. A method for programming a non-planar flash memory array,with shielded floating gates, comprising rows and columns of flashmemory cells, each row of memory cells coupled on a first and a secondplane by a wordline and each column of memory cells coupled on the firstand the second plane, each memory cell having a pair of source/drainregions, a gate insulator, a floating gate, and a control gate, a metalshield layer extending between adjacent wordlines on different planes,the method comprising: biasing the control gate; allowing a firstsource/drain region to float; and biasing the remaining source/drainregion with a positive voltage.
 8. The method of claim 7 wherein biasingthe control gate comprises grounding the control gate.
 9. The method ofclaim 7 wherein the positive voltage is +12V.
 10. The method of claim 7wherein biasing the control gate comprises biasing the control gate witha voltage that is negative with respect to a substrate voltage.
 11. Anelectronic system comprising: a processor that generates memory controlsignals; and a non-planar, flash memory device coupled to the processor,the device comprising: a first plurality of memory cells each comprisinga gate insulator layer formed on a surface of a silicon mesa on asubstrate; a second plurality of memory cells each comprising a gateinsulator layer formed on a surface of a valley between silicon mesas;and metal shielding formed between adjacent wordlines; wherein at leastone memory cell of the first plurality of memory cells and at least onememory cell of the second plurality of memory cells share a commonwordline.
 12. The electronic system of claim 11 wherein the substrate isone of silicon, gallium arsenide, carbon, germanium, orsilicon-on-insulator.
 13. The electronic system of claim 11 wherein thefirst plurality of memory cells is in a first plane and the secondplurality of memory cells is in a second plane.
 14. The electronicsystem of claim 11 wherein the first and second plurality of memorycells are coupled together in a NAND architecture.
 15. The electronicsystem of claim 11 wherein the metal shielding is formed on either sideof and substantially parallel to the wordline.
 16. The electronic systemof claim 11 wherein only a single channel region is under each mesa andonly a single channel region is under each valley.
 17. The electronicsystem of claim 11 wherein the first plurality of memory cells iscoupled to the second plurality of memory cells through source/drainregions of adjacent memory cells.
 18. The electronic system of claim 17wherein the source/drain regions are n+doped regions in a p-typesubstrate.
 19. The electronic system of claim 17 wherein thesource/drain regions are p-drain regions.
 20. An electronic systemcomprising: a processor that generates memory control signals; and aflash memory device coupled to the processor, the device comprising: afirst plurality of memory cells each comprising a gate insulator layerformed on an upper surface of a silicon mesa on a substrate; and asecond plurality of memory cells each comprising a gate insulator layerformed on an upper surface of a valley between silicon mesas.
 21. Theelectronic system of claim 20, wherein each memory cell of the firstplurality of memory cells and each memory cell of the second pluralityof memory cells comprises a control gate coupled to a wordline.
 22. Theelectronic system of claim 21, wherein at least one memory cell of thefirst plurality of memory cells and at least one memory cell of thesecond plurality of memory cells share a common wordline.
 23. Theelectronic system of claim 21, further comprising metal shielding formedbetween adjacent wordlines.
 24. An electronic system comprising: aprocessor that generates memory control signals; and a flash memorydevice coupled to the processor, the device comprising: a first set offlash memory cells formed on a first plane and a second set of flashmemory cells formed on a second plane such that each flash memory cellon the first plane is connected, through a source/drain region, only toan immediately adjacent flash memory cell that is on the second plane.25. The electronic system of claim 24, wherein each flash memory cell ofthe first set of flash memory cells and each flash memory cell of thesecond set of flash memory cells is coupled to a wordline.
 26. Theelectronic system of claim 25, wherein at least one flash memory cell ofthe first set of flash memory cells and at least one flash memory cellof the second of flash memory cells share a common wordline.
 27. Theelectronic system of claim 25, wherein a metal layer is formed betweenadjacent wordlines.